1. Field of the Invention
The present invention relates to a valve timing adjusting apparatus of an internal combustion engine that adjusts valve timing of at least one of an intake valve and an exhaust valve, which is opened and closed by a camshaft with a torque transmitted from a crankshaft, according to a relative phase (hereinafter, referred to as an engine phase) between the crankshaft and the camshaft.
2. Description of Related Art
A previously known valve timing adjusting apparatus changes the engine phase through a planetary movement of a second gear, which is eccentric to and is meshed with a first gear that is synchronously rotated with a crankshaft or a camshaft. Therefore, a rotator, which is coaxial with the first gear and is engaged with the second gear, is rotated relative to the first gear in response to the planetary movement. Japanese Unexamined Patent Publication No. 2005-48706 discloses such a valve timing adjusting apparatus. According to this publication, multiple projections axially project from the second gear and are arranged one after another in a revolving direction of the second gear. Multiple engaging holes, which receive and engage the projections, respectively, are arranged one after another in a rotational direction of the rotator. When a torque is transmitted from the second gear to the rotator through engaged surfaces between the projections and the engaging holes, the rotator is rotated relative to the first gear.
In the valve timing adjusting apparatus disclosed in the above publication, an outer peripheral surface of each projection and an inner peripheral surface of each engaging hole are both cylindrical to implement smooth relative movement therebetween, so that frictional sticking of the projection against the inner peripheral surface of the engaging hole is advantageously limited. However, when the projection engages the inner peripheral surface of the engaging hole at or around a radial line of the second gear, which passes through a center of curvature of the cylindrical outer peripheral surface of the projection, an urging force of the projection, which urges the inner peripheral surface of the engaging hole in the radial direction of the rotator, is increased. This radial urging force does not contribute to the rotation of the rotator and disadvantageously increases a friction between the projection and the inner peripheral surface of the engaging hole, thereby possibly deteriorating a transmission efficiency of the torque. This kind of disadvantage also occurs in a case where the projection engages the inner peripheral surface of the engaging hole at or around a radial line of the rotator, which passes through a center of curvature of the cylindrical inner peripheral surface of the engaging hole.